The situation at Fordow, which has been the focus of the past year’s international nuclear talks with Iran, has created a two-fold nuclear breakout problem. First, having learned how to increase the concentration of enriched uranium to 20 percent, Iran’s nuclear workers can more easily manufacture weapons-grade uranium, which involves further enriching the uranium to a fissile concentration of 90 percent. Second, Iran’s growing stock of 20 percent enriched uranium can be more easily converted to 90 percent highly enriched uranium (HEU) than its stockpiles enriched to the normal 3.5 percent level, which is used by commercial power reactors. ...